Varicella zoster virus (VZV), by virological standards, is one of the most successful of the human herpesviruses. It infects the majority of the human population in childhood and decades later reappears to cause zoster in the aged population. Both diseases are life-threatening in immunocompromised patient and zoster causes long lasting pain and severe ocular disease which can result in blindness. Despite a well-established clinical picture, VZV has remained a difficult virus to study because the virus grows poorly outside the human host. Our research has focussed upon a critical subset of four VZV proteins which are involved in the control of viral gene expression. These proteins, encoded by VZV genes 4, 61, 62 and 63, all activate or repress transcription. Each has multiple functions and it is likely that some act in concert to mediate this control. Proteins from three of these genes (4, 62 and 63) are components of the virus particle, where we hypothesize that they function during the very first events of infection. We propose to examine three additional aspects of these proteins to more clearly understand their structural features and their roles in infection. In Specific Aim l, we propose to identify the parts of the protein designated IE62 which confer its unusual ability to be incorporated in high copy numbers into the VZV virus particle. We will express regions of IE62 in the context of viral recombinants, purify virus from such recombinants and identify which regions retain the ability to be virion incorporated. In the second Specific Aim, we will explore the ability of the transcriptional regulatory proteins to cooperate and interact with one another. Using cellular localization studies and in vitro assays, we will identify the parts of each protein which mediate such interactions. In Specific Aim 3, we plan to address the mechanisms by which gene 4, is made in the infected cell in the absence of further viral protein synthesis. We will test a model in which the gene 4 is activated by specific elements by the virion form of the IE62, we will express altered forms of IE62, a potent transcriptional activator. The long term goal of these studies is to understand the functions of these proteins so that novel antiviral agents can be developed to inhibit their functions and thus, halt VZV disease.